Senior sources in Sierra Leone believe Britain is about to freeze a £15m payment to the West African nation amid evidence of endemic corruption that has seen millions of pounds in aid line the pockets of dishonest officials while ordinary people struggle in conditions of catastrophic poverty .

Britain, as the single largest donor country, gives the small country more than £50m a year, including £12m for its armed forces and the £15m direct payment to the Treasury, which is due in July to cover public servants' salaries.

A Foreign Office source claimed that the July payment will not be released. But a source for the Department for International Development (Dfid) disputed this last night, insisting the 'payment will be released' but admitted that some concerns remain about the ability of the Sierra Leone government to meet certain requirements such as accounting for the aid they receive and reaching certain benchmarks.

Ten days ago Blair visited the country on his farewell Africa tour and said things were 'a darn sight better' than five years ago. But people in Freetown were disappointed that he did not travel to the decrepit capital, opting instead to limit his six-hour visit to the area around the international airport at Lungi.

Morlai Kamara, a good-governance campaigner with the Network Movement for Justice and Development in Freetown, said corruption was widespread. 'It permeates every level from the office of the President lawyer to the cleaner. It takes the form of people embezzling funds, appointing people they know and abusing resources. Endemic corruption was one of the main reasons for the war: the government could no longer meet its side of the social contract. Now we are back at pre-war levels.'

In the past few years, chiefly thanks to British lobbying, Sierra Leone has benefited from more international concern than almost any other country. Towards the end of the war it had the world's biggest UN peacekeeping presence - more than 17,000 troops. Britain's high-profile military engagement involved the Paras, Navy, Gurkhas and the SAS and, at the time, was the most expensive British military campaign since the Falklands. Later millions of pounds were pledged to create an army and police force and see through disarmament programmes for 56,000 combatants, including children.

Yet Freetown remains a metropolitan slum, without electricity or drinking water, where living conditions are worse for many than they were during the war. Promised plans by the government - for which aid was paid - to kick-start agriculture in the interior of the country have not materialised. Next month's planned presidential and parliamentary elections have been delayed until August and the reason given - the expected weather - has failed to convince the people.

In the diamond-rich Kono district, miners are still sifting river beds for elusive gems. Diamond exports are now taxed but the revenue is not, as was promised, being spent on building schools and clinics.

Just as before and during the war, Sierra Leone has the worst children's and maternal mortality figures in the world. Life expectancy stands at 41.

Val Collier, former commissioner of the country's Anti-Corruption Commission, said Britain and other aid donors were hypocritical: 'When money is given, checks and balances should be imposed. A large share of the money is spent on sending foreign consultants here to write reports; they come with their laptops in their slingbags, like intellectual mercenaries. Such spending does not put food in the bellies of the people of Sierra Leone.'

The new commissioner, Henry Joko-Smart, is seen as government-friendly and his work has proved timid. A Dfid report on the commission last month found that, of 64 cases examined in 2006, 15 were pursued, including a case against a hospital payroll officer and another against a headmaster. Corruption at other levels was ignored.

A Foreign Office official confirmed the freeze on Dfid's £15m payment, due next month, to the Sierra Leone government's 'consolidated fund', which pays public servants' salaries. 'We want accountability,' said one source. But a spokesman would only confirm that the matter was under discussion.